(1) Field of the Invention
This invention relates to a system for mounting and removal of electronic type load cells of the type used in heavy capacity industrial weight scales. In addition to the accurate and stable mounting of the load cells the system provides a means for the selective application or removal of the weight normally applied to the load cells. The system thus facilitates the testing, calibration, and replacement of the load cells.
(2) Description of Related Art
Historically, the typical method of weight scale calibration consisted of adjustment of the scale to a zero reading with only the dead weight (the weight of containers and apparatus which are a permanent part of the scale) applied, and then to apply various known weights to the scale while making appropriate adjustments to the scale after the addition of each weight. This calibration method remains popular for smaller scales, and surprisingly remains in some use even on heavy capacity industrial scales. The problems commensurate with use of such a method for heavy capacity scales increase astronomically as the capacity of the scale to be calibrated increases. One can readily appreciate, for example the logistics of fabrication, transportation and handling a weight of many tons in an industrial environment.
Another and more sophisticated method of calibrating heavy capacity scales is called a "Force Calibration System". Systems of this type are designed to apply a measured force to the scale. These systems are extremely expensive to build and to use. The force which is applied to the scale is normally created by use of hydraulic jacks acting through cumbersome fixtures which are limited in the force which they can withstand. Thus, in many cases a heavy capacity scale can only be calibrated over a small portion of its rated capacity. Further, such systems have no means for including either dead weight or inherent site environmental problems such as uneven scale foundations in the calibration process.
State of the art electronic scales use load cells to provide the primary signals which, after appropriate processing, actuate the scale displays.
A load cell is a precision machined metallic device which will deflect under load and return to normal state when unloaded. Strain gages are affixed to the sensitive area of the device to measure the amount of deflection which occurs under load. The deflection of the cells is quite small, seldom exceeding 0.010 of an inch. The strain gages, in conjunction with appropriate electronic apparatus, produce a signal which varies proportionally and linearly as the weight applied to the load cell is varied. This signal is processed and fed to a display which reads the weight being applied to the cell. Industrial scales typically utilize a plurality of load cells for each weighing application. For example, a liquid tank would normally be supported by four legs with a load cell located under each leg.
Load cells may be basically categorized as working load cells, which remain in a scale apparatus during normal use, and as calibration load cells, which are employed for the calibration or testing of work cells. These types of load cells may be referred to as load bearing members in that each type is required to bear the entire weight being weighed by that load cell during a weighing operation.
Recent technology has produced a calibration procedure which is capable of testing and calibrating electronic load cells while in place. However, heretofore no effective means has been provided for the efficient utilization of such a system. The load cells often bear a great deal of weight and thus present a formidable problem of proper mounting of the load cells and of lifting the weight from the load cell when testing, calibration or replacement is required. The present invention provides a mounting and removal system for load cells, which system resolves the shortcomings of the prior art by permitting the efficient and economical use of modern load cells.